1. Field of the Invention
This invention relates to a control method for an open channel of a single stage or a plurality of stages in which the condition of water flowing therethrough undergoes a transient change due to variations in a flow rate of diverted water from each stage or reach of the open channel, the term "reach" meaning each space defined between two gates of the open channel.
2. Description of the Prior Art
In various types of water supply, particularly a supply of water for irrigation purposes, the flow rate of diverted water from each reach of an open channel would show a variation due to fluctuations in the demand for water which would be caused to occur irregularly from time to time by weather conditions or other factors. It is impossible to directly measure such variations. A water supply through an open channel is controlled for the purpose of providing the open channel with a stable water flow condition free from the risks of overflow while ensuring that a flow rate of water large enough to meet the demand flows through the open channel by adjusting for fluctuations in demand.
Heretofore, it has been usual practice to use a control method wherein the relation between the liquid level in a reach and the degree of opening of a gate is represented by using a simple model, or a "first order lag plus dead time" system and expressed by using a transfer function, so as to control the water flow to keep the liquid level constant. This method of control has suffered the disadvantage that, when the flow condition of water through the open channel shows a great transient change due to variations in the flow rate of diverted water, the model shows a large error and it becomes impossible to control the flow condition of water in a manner to enable the aforesaid purpose.
To serve the aforesaid purpose, one would have to collect information on the transient condition of the flow of water through the open channel from moment to moment. If the prior art were intended to obtain with a high degree of precision the transient condition of water flow through the open channel, the following equations would have to be solved: ##EQU1## where V: flow velocity.
Q: flow rate. PA0 h: depth of water. PA0 R: hydraulic radius. PA0 n: roughness coefficient. PA0 A: cross-sectional area of channel. PA0 i: gradient of bottom. PA0 g: graviational acceleration.
These equations should be solved numerically because it is impossible to solve them analytically. The calculation involved is referred to as an indefinite flow calculation and requires a great number of calculations to be performed by using a large computer. Because of this, it has hitherto been impossible, due to limitations placed by calculation times, to obtain the transient condition of flow of water through an open channel by applying the indefinite flow calculation directly to on-line processing.